Diaphragm valves for use in irrigation systems typically have an inlet opening, an exit opening and a diaphragm element having a seal positioned to selectively open and close against a generally cylindrical diaphragm seat to permit or block fluid flow through an opening of the diaphragm seat and thus from the inlet opening to the outlet opening. A control chamber is positioned on the opposite side of the diaphragm element from the seat to control the position of the seal of the diaphragm element. When the fluid pressure acting on the diaphragm element from the control chamber side exceeds the fluid pressure acting on the opposite side of the diaphragm element, the diaphragm element will be forced against the diaphragm seat to block fluid flow through the opening of the seat and thereby block fluid flow from the inlet opening to the outlet opening. Conversely, when the fluid pressure acting on the diaphragm element from the control chamber side is less than the fluid pressure acting on the opposite side of the diaphragm element, the diaphragm element will be forced away from the diaphragm seat to permit fluid flow through the opening of the seat and thereby permit fluid flow from the inlet opening to the outlet opening.
The seal of the diaphragm element often engages an annular face of the diaphragm seat when the diaphragm element is in its closed position to block fluid flow through the opening of the seat and to the outlet opening. As the diaphragm element moves from its open position to its closed position, the flow area between the diaphragm seat and the seal continually decreases in correspondence with the spacing of the seal from the diaphragm seat until the seal is engaged with the diaphragm seat to block flow through the opening of the diaphragm seat and to the outlet opening. When the seal engages the diaphragm seat to block flow through the opening of the diaphragm seat, the abrupt change in the flow area between the seal and the diaphragm seat from greater than zero, immediately prior to engagement, and zero, at the time of engagement, can cause a sudden pressure spike greater than the upstream pressure. More specifically, the pressure spike in the upstream pressure can be caused as the motion energy in the flowing fluid is abruptly converted to pressure energy acting on the components of the diaphragm valve. This pressure spike can cause the diaphragm valve to experience a water hammer effect, which can undesirably result in increased stress on the components of the diaphragm valve, as well as other components of the irrigation system, and can lead to premature failure of the components.
An attempt to address the water hammer effect is disclosed in U.S. Pat. No. 5,104,090 (“the '090 patent”). The '090 patent discloses V-shaped radial grooves provided on an outer surface of a diaphragm. However, the diaphragm of the '090 patent is configured such that the grooves are generally downstream of the valve seat, which can undesirably permit debris, such as grit and the like, to pass the valve seat before reaching the grooves. Accumulation of debris on the valve seat can have a negative impact on the seal between the diaphragm and the valve seat, such as by abrading the portion of the diaphragm that repeatedly contacts the valve seat.
In order to control the pressure in the control chamber, a fluid entrance path and a fluid exit path to and from the control chamber are typically provided. The fluid entrance path may extend between the inlet opening and the control chamber, and may be continuously supplied with fluid from the inlet opening. The fluid exit path may extend between the control chamber and the outlet opening. A selectively actuable control valve may be positioned to block fluid flow through the fluid exit path.
When the control valve is positioned to block fluid flow through the fluid exit path from the control chamber, the fluid entrance path continues to permit fluid to flow from the inlet opening to the control chamber, thereby causing fluid to accumulate in the control chamber. The building pressure in the control chamber pushing down acts on the whole upper surface of the diaphragm assembly. The underside of the diaphragm assembly only sees the high pressure outside the radius of the seat cylinder. The fluid flowing through the restriction between the diaphragm assembly and the valve seat undergoes a drop in pressure as it passes through the restrictive aperture. The underside of the diaphragm, inside of the seat radius, sees only this reduced pressure. Therefore, as the downward force due to the building pressure acting on the entire upper surface of the diaphragm assembly exceeds the upward force of the inlet pressure acting only on the underside area outside the seat radius, the diaphragm assembly begins to descend and eventually closes the valve.
When the control valve is positioned to permit fluid flow through the fluid exit path from the control chamber, fluid exits the control chamber at a faster rate than fluid enters the control chamber. This causes the fluid pressure acting on the control chamber side of the diaphragm element to decrease relative to the fluid pressure acting on the side of the diaphragm element facing the inlet opening. The fluid pressure in the inlet opening then causes the diaphragm element to move to its open position, whereby the seal of the diaphragm element is spaced from the diaphragm seat and fluid flow is permitted from the inlet opening, through the opening of the diaphragm seat and through the exit opening.
During installation and operation of the diaphragm valve, air can become trapped in the control chamber. The presence of excess air, a compressible fluid, in the control chamber can adversely effect the operation of the diaphragm valve, and in particular the shifting of the diaphragm element between its open and closed positions. For example, excess air in the control chamber can allow the diaphragm element to shift from its open position to its closed position more rapidly than intended, which can further exacerbate the water hammer effect discussed above. In order to permit for air to be removed from the control chamber, diaphragm valves are often provided with manually-operated bleed mechanisms that allow for a user to selectively vent air from the control chamber.
One example of a manually-operated bleed mechanism is disclosed in U.S. Pat. No. 6,079,437 (“the '437 patent”). The '437 patent discloses a flow control stem that is pushed downwardly relative to a bonnet to position an o-ring seated in a groove in the flow control stem away from a shoulder of the bonnet to permit fluid to vent therepast through a vent gap. However, in such an arrangement the o-ring could undesirably become unseated from the groove of the flow control stem due to the pressure of the venting fluid. If the o-ring is unseated, the resealing of the vent gap can inadvertently occur during venting, resulting in a diaphragm valve that does not properly vent and thus not properly operate.
Another drawback of typical diaphragm valves is that their diaphragms are often internally reinforced with fibers or made from a more expensive, specialized material, which can add to the cost of the diaphragms. However, if the internal reinforcements were simply removed, the diaphragm could stretch in an uncontrolled manner in response to fluid pressure, particularly in the case of reverse-flow diaphragm valves.
In view of the foregoing deficiencies in existing diaphragm valves, there remains an unmet need for diaphragm valves having improved flow, including diaphragm valves configured to reduce the water hammer effect and/or improve bleed operation and configured for reduced manufacturing and materials costs.